With the increasing popularity of wide area networks (WAN5), such as the Internet and/or the World Wide Web, network growth and traffic has exploded in recent years. Network users continue to demand faster networks and more access for both businesses and consumers. As network demands continue to increase, existing network infrastructures and technologies are reaching their limits.
An alternative to present day hardwired or fiber network solutions is the use of wireless optical communications. Wireless optical communications utilize point-to-point communications through free-space and therefore do not require the routing of cables or optical fibers between locations. Thus, wireless optical communications are also known as free-space or atmospheric optical communications. For instance, in a FSOCS, a beam of light is directed through free-space from a transmitter at a first location to a receiver at a second location. Data or information is encoded into the beam of light, and therefore, the information is transmitted through free-space from the first location to the second location.
Transmission of optical signals through free space poses many challenges. Notably, atmospheric conditions can greatly degrade signal strength, and consequently, reduce the maximum link distances. Also, when launching a single-mode beam from a free-space optical terminal using conventional means, atmospheric scintillation and other wavefront distortion cause the beam to break up into chaotic bright and dark spots. Stated another way, such beams generally have non-uniform power distributions that vary on a timescale of milliseconds (corresponding to the transit time of wind passing through the free-space beam).
In some FSOCS applications, non-uniform power distributions far from the transmitter tend to undesirably limit the permissible overall power of the optical signal because the peak possible irradiance must meet specified eye safety standards. For example, some FSOCS applications must comply with specified laser classifications that address eye safety standards, such as the laser classifications defined by International Electrotechnical Commission (IEC) International Standard 60825-1: 1993+A1:1997+A2. To comply with the applicable standard(s), the power of the transmitted signals must be limited such that the peak possible irradiance received at a person's eye is maintained below the specified maximum value.